<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>计算器</title>
</head>
<body>
<button onclick="alert('警告框')">弹出警告</button>
<button onclick="confirm('您确认要删除嘛')">弹出确认框</button>
<button onclick="prompt('请输入会员号')">弹出提示输入框</button>
<hr>
<input type="text" placeholder="请输入数字1" id="i1"><br>
<input type="text" placeholder="请输入数字2" id="i2"><br>
<button onclick="calc('+')">加</button>
<button onclick="calc('-')">减</button>
<button onclick="calc('*')">乘</button>
<button onclick="calc('/')">除</button>
<h4>运算结果：<span></span></h4>
<script>
    function calc(o){
       let n1=document.getElementById('i1').value;
       let n2=document.getElementById('i2').value;
       n1=parseFloat(n1);
       n2=parseFloat(n2);
       let spanE=document.querySelector('span');
       switch (o) {
           case '+':
               spanE.innerHTML=n1+n2;break;
           case '-':
               spanE.innerHTML=n1-n2;break;
           case '*':
               spanE.innerHTML=n1*n2;break;
           case '/':
          if (n2!=0){
              spanE.innerHTML=n1 / n2
          }else {
              alert('除数不能为0')
          }
       }

    }
</script>
</body>
</html>